The team, experts in biology and biochemistry, sampled water from 100 private water wells in North Texas and found the highest levels of the toxic metals – in some cases levels above what's considered safe by the EPA – in the wells closest to gas drilling operations, according to the study by University of Texas Arlington researchers.

The metals they were testing for – arsenic, selenium and strontium – can occur naturally in water. But the team pointed to the trend of higher levels being found closest to active gas wells as suggesting that the industrial activity could have released chemicals into the groundwater feeding the wells.

According to a release about the study from the university:

“Researchers believe the increased presence of metals could be due to a variety of factors including: industrial accidents such as faulty gas well casings; mechanical vibrations from natural gas drilling activity disturbing particles in neglected water well equipment; or the lowering of water tables through drought or the removal of water used for the hydraulic fracturing process. Any of these scenarios could release dangerous compounds into shallow groundwater.”

UT Arlington associate professor of chemistry and biochemistry Kevin Schug led the team of researchers. Dr. Brian Fontenot, whose degree is in quantitative biology, was lead author on the paper.

"This study alone can't conclusively identify the exact causes of elevated levels of contaminants in areas near natural gas drilling, but it does provide a powerful argument for continued research," said Fontenot, a UT Arlington graduate.

The team gathered the samples in 2011 from a 13-county area in North Texas, where gas companies have been drilling, fracking, for natural gas for several years.

Most of the samples, 91, were taken near active drilling areas with one or more gas wells within a five kilometer radius. Nine control samples were taken from sites more than 14 kilometers from a natural gas drilling operation, in or outside the Barnett Shale region which spans the Dallas/Fort Worth metroplex.

A gas well in North Texas.

The water composition was compared to historical records covering the 20th Century and analyzed by gas chromatography at the UT Arlington Shimadzu Center for Advance Analytical Chemistry.

Tests showed that 29 of the water wells that were near active gas drilling exceeded the EPA's EPA's Maximum Contaminant Limit (MCL) of 10 micrograms per liter for arsenic. One water sample was contaminated with 161 micrograms per liter — 16 times the EPA's MCL for drinking water.

Longterm exposure to unsafe levels of arsenic in water "has been linked to cancer of the bladder, lungs, skin, kidneys, nasal passages, liver and prostate," according to the EPA's arsenic info sheet.

Other findings reported by the team:

10 samples taken from near gas well activity showed selenium levels higher than the historical average. Two samples exceeded the EPA's safety standard for selenium, which can cause negative health effects if consumed at levels considered unsafe.

Strontium, found in almost all the samples, was "significantly higher" than historical levels in the areas of natural gas extraction. Seventeen samples from the gas drilling areas and one from outside the active gas drilling area exceeded the safe level of 4,000 micrograms per liter set by the Agency for Toxic Substances and Disease Registry. Exposure to higher than recommended levels of strontium is believed to impair bone growth in children, according to the agency.

The areas outside of active drilling sites, or outside the Barnett Shale, did not show elevated levels for most of the metals.

Researchers also found traces of the man-made solvent methanol and ethanol in nearly one-third of the water samples.

Other leaders of the team were Laura Hunt, who conducted her post-doctoral research in biology at UT Arlington, and Zacariah Hildenbrand, who earned his doctorate in biochemistry from the University of Texas at El Paso and performed post-doctoral research at UT Southwestern Medical Center.

Hildenbrand is also the founder of Inform Environmental, LLC. Fontenot and Hunt work for the EPA regional office in Dallas, but the study is unaffiliated with the EPA and each received permission to work on the water contamination project outside the agency, according to UT Arlington, a campus of about 33,000 students located between Dallas and Fort Worth.